A fine-grained multi-source measurement platform correlating routing transitions with packet losses

Abstract

In this paper, we are interested in the relationship between packet losses and routing changes in an operational network. To do so we designed and deployed DCART, a monitoring platform over RENATER, the French research and education network. Our platform collects four data sources using both active and passive measurements in order to unveil their temporal correlations. Active probing allows especially for measuring packet losses on specifically crafted data flows. Those flows explore several load balanced paths and ease the revelation of forwarding loops. Passive monitoring is achieved by listening to all routing updates from IS-IS, the intra-domain routing protocol in use, and by retrieving tickets generated by the Network Operations Center (NOC).During our monitoring campaign, we observe that most of the series of loss were correlated to routing events either because routing changes lead to inconsistent state transitions, or because faulty – and so lossy – links trigger numerous periods of link flapping. In particular, we show that losses due to forwarding loops resulting from inconsistent routing states are quite common when links come back after an outage. We also show that link flapping sometimes induce very long lasting lossy periods frequently unnoticed by the NOC. A lightweight monitoring platform such as DCART could be used to better anticipate recurrent network outages and to improve the ticketing system.